This invention relates broadly to gauges for measuring the level of liquid in a tank; in particular, a float-type liquid level gauge for measuring the level of liquid in a tank containing a liquefied gas. More particularly, this invention relates to single piece magnetic cap with alignment feature for use with a float-type liquid level gauge.
This invention relates generally to a liquid level gauge, and more particularly to gauges commonly used for measuring liquefied petroleum gas (LPG) type liquids. The LPG is typically stored as a liquid under pressure in a tank or cylinder. A liquid level gauge may be provided on the tank or cylinder for measuring the level of the liquid.
A typical gauge of this type utilizes a pivoting float arm having a float at one end and an opposing separately attached counterweight at another positioned on a opposing side of a pivot from the float. The pivoting float arm moves in response to changes in the liquid level inside the tank. As the float arm pivots, it rotates a gear assembly which turns a drive shaft located in a support arm that is connected to the float arm. The drive shaft is connected to a tank magnet which is magnetically coupled to a receiving magnet in a gauge head. As the drive shaft rotates and rotates the tank magnet, the magnetic flux of the tank magnet rotates the receiving magnet which moves an external liquid level visual indicator, such as a pointer on a dial. Examples of such gauges are disclosed in U.S. Pat. Nos. 6,089,086 and 6,041,650.
In assembling these gauges, it is necessary to align the tank magnet on the end of the drive shaft with a base position of the float arm so that accurate readings will be transferred to the dial assembly. It is important that when the gears connected to the drive shaft in the support arm and the gears connected to the float arm are attached, they are attached at such a position that the tank magnet is aligned to provide an accurate reading of the level of liquid in the tank. Previously, this alignment was done manually by rotating a round drive shaft until the position of the tank magnet on the drive shaft corresponded to the given location of the float arm. At that point, the drive shaft was staked to the gear, permanently attaching the gear to the drive shaft and ensuring that the alignment of the magnet did not change. Further, the magnet needs to be installed in and secured to a magnet holder or other attachment device prior to the magnet holder being secured to the drive shaft in the support arm. The extra step of assembling the magnet and the magnet holder add extra work in the installation and potentially create an opportunity for inaccuracy in alignment and incorrect readings. Additionally, attaching a separate counterweight piece to the float arm requires an additional assembly step and an accurate determination of size, weight, and positioning so as to provide the proper balance to the float arm.
Not surprisingly, there are problems with this assembly. Improper alignment of the magnet in the magnet holder can reduce the accuracy of the gauge. Further, it takes time to align the tank magnet to the corresponding position of the float arm. Even then, the accuracy could be compromised if the drive shaft was inadvertently turned before or while the stake is being inserted.
There is a continuing need for a gauge that can be assembled more efficiently and with reduced risk of error in the proper alignment of the magnet. In view of this need, this invention provides for a gauge that can be aligned in a trouble free and accurate way, allowing assembly to be more efficient.
In accordance with one aspect of the current invention, a linkage is provided including a pinion gear, a second gear, and a gear housing. The pinion gear, located in the passageway of the first portion of the gear housing, has a pinion gear neck and an engaging means. The second gear, rotatably attached to the second portion of the gear housing, also has engaging means which mesh with the engaging means of the pinion gear.
In another aspect of the current invention, a linkage is provided comprising a pinion gear, a second gear and a gear housing. In this aspect of the invention, the pinion gear has a pinion gear neck, pinion gear teeth, and a pinion gear nose. The first portion of the gear housing has a passageway for insertion of the pinion gear neck as well as an appendage, such as a support arm. The second portion of the gear housing has a slot to allow the pinion gear teeth unencumbered rotation. The second portion of the gear housing also has a notch for the pinion gear nose to rotate freely. The second gear is rotatably attached to the second portion of the gear housing and the engaging means of the second gear mesh with the teeth of the pinion gear.
In yet another aspect of the current invention, an apparatus for use with a liquid level gauge is provided. The apparatus comprises a pinion gear, a second gear, and a gear housing. The pinion gear neck defines a shaped passageway to accommodate a similarly shaped drive shaft. The pinion gear neck is inserted into a recess in the passageway in the gear housing. As an additional feature, the neck of the pinion gear could be longer than the recess so the pinion gear is more secure in the gear housing. A bushing could also be inserted into the passageway so as to further stabilize the pinion gear. In a further embodiment, the second gear has a nose that is inserted into a receiving passage of the gear housing as a way to rotatably attach the second gear to the gear housing. An alternative could be for the gear housing to have a nose that is inserted into a passage on the second gear. The second gear could also be adapted for use as part of a pivot arm assembly.
In yet another aspect of the current invention, a drive shaft assembly is presented. The drive shaft assembly comprises a drive shaft which has a positioning feature. This positioning feature limits the number of ways the drive shaft can fit into the passageway in the neck of the pinion gear. A magnet holder and a magnet are located on the end of the drive shaft opposite the end that is inserted into the pinion gear neck.
In a still further embodiment, a liquid level gauge is provided including a gauge head, a support arm, a gear housing, a drive shaft assembly, a pivot arm assembly, and a tank magnet. The pivot arm assembly is rotatably connected to the gear housing. The gear housing is attached to the lower end of the support arm and the gauge head is connected to the upper end of the support arm. An internal passageway for insertion of the drive shaft is located in the support arm and continues into the lower portion of the gauge head. In a further embodiment, the drive shaft can be of variable length so different length support arms can be utilized. The tank magnet is attached to the upper end of the drive shaft assembly inside the gauge head. Angular motion of the pivot arm relative to the support arm imparts rotational motion to the drive shaft via the gears, and thus to the tank magnet attached to the drive shaft. In a further embodiment, the pivot arm assembly can also include a counterweight arm and a separately attached counterweight positioned at an opposing end and on an opposing side of the pivot from the float arm and float. However, it is conceivable that the counterweight arm itself could act as the counterweight providing proper balance without need for a separately attached counterweight.
In yet another aspect of the invention, a single piece magnetic cap having an alignment feature to insure that the tank magnet and the dial magnet are quickly and accurately aligned in a predetermined arrangement. The magnetic cap defines a bore shaped to accept a shaped drive shaft. The magnetic cap further includes an alignment feature corresponding to an alignment feature on the shaped drive shaft. When drive shaft is properly installed within the bore of the magnetic cap, the alignment feature on the drive shaft engages the alignment feature of the magnetic cap thereby preventing rotation of the magnetic cap with respect to the drive shaft and thereby providing the predetermined alignment of the magnetic cap (tank magnet) with respect to the dial magnet. The magnetic cap is preferably molded from a ferritic material, such as ferrite powder, and a durable medium, such as nylon. The single piece magnetic cap can be quickly and inexpensively formed in any desirable shape, size, or configuration and formed to accommodate attachment to any shape or dimension shaft. The engaging portion of the drive shaft could be an engaging edge, a protrusion or a groove which would correspond to an accepting portion within the bore of the magnetic cap.